Flip chip mounting method by no-flow underfill having level control function

ABSTRACT

In a flip shop mounting method by no-flow underfill in which resin  54  is pre-coated on a substrate  52 , and a semiconductor  50  with bump is mounted on the substrate  52  to join a pad electrode  53  on the substrate  52  to the bump  51 , the substrate  52  is placed on an upper surface of a base  11  of a reflow jig  10 , the resin  54  highly filled with filler  55  is applied onto the substrate  52 , the semiconductor  50  with bump is mounted at a predetermined position over the substrate  52 , a press plate  21  is placed on an upper portion of the semiconductor  50 , a spacer  13  is interposed between a lower surface of the press plate  21  and an upper surface of the base  11  to regulate an amount of press force of the press plate  21 , and horizontal movement of the press plate  21  is regulated by positioning guide pins  15  on the upper surface of the base  11.

TECHNICAL FIELD

The present invention relates to a flip chip mounting method by no-flowunderfill and, more particularly, to a flip chip mounting method by ano-flow underfill in which, when a resin highly filled with a filler ispre-coated on a substrate, a bump is brought into reliable contact witha bump electrode without sandwiching the filler between the bump of asemiconductor and a pad electrode on the substrate to make it possibleto reliably perform reflow soldering.

BACKGROUND ART

In recent years, with a reduction in size of electric devices, in orderto improve a space-saving property and electric characteristics,semiconductors are frequently mounted on substrates by a flip chipmounting method. In the flip chip mounting method, a projectionelectrode called a bump is formed on a terminal electrode formed on arear surface of a semiconductor chip, a semiconductor is fixed to thepad electrode formed on the substrate through the bump to achieveelectric conduction.

The bump consists of a solder material or the like. However, since ajunction area is small, a mounting strength often lacks. In addition,distortion occurs due to a difference or the like between coefficient ofthermal expansions of the substrate and the semiconductor, and the bumpmay be fall off from the pad electrode because of mechanical shock orthermal shock. Therefore, in order to improve the joint strength, afterthe bump is joined to the pad electrode on the substrate by thermalwelding, an underfill process which pours an epoxy-based resin into agap between the semiconductor and the substrate and then thermally curesthe resin is performed.

However, since the underfill process requires heating processes forconnection between electrodes by soldering and curing of the resin andincludes a large number of heating steps to increase the cost.Furthermore, workability for pouring a resin from a side of the gapbetween the semiconductor and the substrate is poor, a space for pouringthe resin is necessary. The underfill process is disadvantageous to areduction in size of an electric device.

In order to solve the drawback, the following mounting method by ano-flow underfill is proposed (for example, see Patent Document 1). Thatis, a resin is pre-coated on a substrate, and, thereafter, asemiconductor with bump is pressed onto the substrate to spread thepre-coated resin so as to bring the bump and the pad electrode intocontact with each other. In this state, the resultant structure isheated to perform connection between the electrodes and curing of theresin by performing a heating step once.

In this case, powder such as alumina powder or silica powder calledfiller is mixed in the epoxy-based resin used in the underfill processor the no-flow underfill process to increase the strength of the resin.In the underfill process, since a resin is poured after the bump isjoined to a pad electrode, the filler does not adverse affect the resin.

However, in the no-flow underfill process, as shown in FIG. 7, since thebump 51 is brought into contact with the pad electrode 53 of thesubstrate 52 by only the weight of the semiconductor 50, the filler 55mixed in resin 54 is sandwiched between the bump 51 and the padelectrode 53, and a gap may be formed between the bump 51 and the padelectrode 53. In the no-flow underfill process, since connection betweenelectrodes and curing of the resin are performed in the same heatingstep, when the gap is formed between the bump 51 and the pad electrode53, the gap is filled with the resin 54 not to achieve electricconduction.

As shown in FIG. 8, when the semiconductor 50 is forcibly pressed to thesubstrate 52 by the heavy weight 56 or the like, the filler 55 ispressed out, or electric conduction between the bump 51 and the padelectrode 53 is assured while convoluting the filler 55. However, inthis state, when reflow soldering is performed, after the bump 51 isthermally welded on the pad electrode 53, the weight of the heavy weight56 continuously operates. For this reason, the bump 51 may be broken bypressure, or the bump may run out of the pad electrode 53 to causeelectric short circuit.

As a configuration using a heavy weight in the no-flow underfillprocess, the following apparatus and method are known. That is, a resincontaining spherical particles is applied onto an upper surface of asubstrate, and the spherical particles are arranged in a region betweenpad electrodes, a heavy weight is placed on an upper portion of asemiconductor to perform reflow soldering without any change (forexample, see Patent Document 2).

Patent Document 1: Japanese Unexamined Patent Publication No. 10-125724

Patent Document 2: Japanese Unexamined Patent Publication No. 2001-53109

DISCLOSURE OF THE PATENT

The invention according to Patent Document 1, a resin is pre-coated on asubstrate, connection between electrodes and curing of the resin areperformed by performing a heating step once. For this reason, areduction in cost is achieved by simplifying steps. However, as shown inFIG. 7, the filler mixed in the resin is sandwiched between the bump andthe pad electrode, and electric conduction may not be achieved. When thefiller mixed in the resin is lessened or the resin is not mixed, adrawback caused by sandwiching the filler can be solved. However, thestrength of the resin may be deteriorated to break the bump.

The invention according to Patent Document 2, filler is pressed out by aheavyweight, or the filler is convoluted to assure electric conductionbetween a bump and a pad electrode. At the same time, sphericalparticles are mixed in a resin to hold an interval between asemiconductor and a substrate at a predetermined size. However, thespherical particles are not always accurately arranged in a regionbetween pad electrode, and the heavy weight may be displaced.

Therefore, it is an object of the present invention to make it possibleto bring a pad electrode of a substrate into reliable contact with abump to reliably perform reflow soldering when a resin highly filledwith a filler is pre-coated on a substrate to mount a semiconductor.

The present invention has been proposed to achieve the above object. Aninvention according to a first aspect provides a flip chip mountingmethod obtained by a no-flow underfill having a level control functionin which a resin is pre-coated on a substrate, and, thereafter, asemiconductor with bump is mounted on the substrate to join a padelectrode of the substrate to the bump, wherein the substrate is placedon an upper surface of a base of a reflow jig, a resin highly filledwith the filler is applied to the substrate, the semiconductor with bumpis mounted at a predetermined position of the substrate, a heavy weightlarger than an overall size of a product of the substrate is placed onupper portion of the semiconductor, and a spacer is interposed between alower surface of the heavy weight and the upper surface of the base toregulate an amount of press force of the heavy weight, and horizontalmovement of the heavy weight is regulated by a positioning guide uprightstanding on the upper surface of the base.

According to this configuration, when the semiconductor is mounted suchthat the resin highly filled with the filler is pre-coated on thesubstrate, the heavy weight placed on the upper portion of the substrateforcibly presses the semiconductor onto the substrate, and horizontalmovement of the heavy weight is regulated by the positioning guide. Forthis reason, the bump is accurately pressed onto the pad electrodewithout displacement of the bump.

In this state, when reflow soldering is performed, even though thefiller mixed in a resin is sandwiched between the bump and the padelectrode, the heavy weight forcibly presses the semiconductor to thesubstrate. For this reason, the filler is pressed out from a portionbetween the bump and the pad electrode, and the bump is reliably joinedto the pad electrode by thermal welding. Alternatively, the sandwichedfiller is pressed from above while being convoluted between the bump andthe pad electrode, and the bump is reliably joined to the pad electrodeby thermal welding. Since a spacer is interposed between the lowersurface of the heavy weight and the upper surface of the base, an amountof press force of the heavy weight is regulated even though the bump isthermally welded. The bump is not broken by pressure, or the bump doesnot run out of the pad electrode not to cause electric short circuit.

The present invention, as described above, even though the filler mixedin the resin is sandwiched between the bump and the pad electrode, thefiller can be prevented from being pressed out by pressing thesemiconductor by the heavy weight, or a gap can be prevented from beingformed between the bump and the pad electrode while convoluting thefiller. For this reason, reflow soldering is performed to assureelectric conduction between the bump and the pad electrode. Horizontalmovement of the heavy weight is regulated by a positioning guide,displacement does not occur. Furthermore, an amount of press force isregulated by the spacer, the bump can be prevented from being broken bypressure.

The present invention can contribute to improvement of workability andreliability in a flip chip mounting method by a now-flow underfill.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a reflow jig used in amounting method according to the present invention.

FIG. 2 is an explanatory pattern diagram showing an assembling state ofthe reflow jig in FIG. 1.

FIG. 3 is an explanatory diagram showing operation processes of thereflow jig in FIG. 2.

FIG. 4 is an explanatory diagram showing a final process of the reflowjig in FIG. 2.

FIG. 5 is an explanatory diagram showing other operation processes ofthe reflow jig in FIG. 2.

FIG. 6 is an explanatory diagram showing a final process of a reflow jigin FIG. 5.

FIG. 7 is an explanatory pattern diagram showing a defect of aconventional no-flow underfill process.

FIG. 8 is an explanatory pattern diagram showing an example which solvesthe defect in FIG. 7 by a heavy weight.

BEST MODE FOR CARRYING OUT THE INVENTION

A flip chip mounting method obtained by a no-flow underfill according tothe present invention will be described below with reference topreferred embodiments. When a resin highly filled with the filler ispre-coated on a substrate to mount a semiconductor, a bump is broughtinto contact with a pad electrode of the substrate at a correct positionto make it possible to reliably perform reflow soldering. In order toachieve the above object, according to the present invention, thesubstrate is placed on an upper surface of a base of the reflow jig, aresin highly filled with the filler is applied onto the substrate, thesemiconductor with bump is mounted at a predetermined position of thesubstrate, and a heavy weight larger than an overall size of the productis placed on an upper portion of the semiconductor. At the same time, aspacer is interposed between the lower surface of the heavy weight andthe upper surface of the base to regulate an amount of press force ofthe heavy weight, and horizontal movement of the heavy weight isregulated by a positioning guide upright standing on the upper surfaceof the base.

FIG. 1 is an exploded perspective view of a reflow jig 10 used in themounting method according to the present invention. The reflow jig 10 isconstituted by a base 11 on which a substrate 52 is placed and a pressplate 21 arranged above the base 11 to mount a semiconductor 50 on thesubstrate 52.

On the upper surface of the base 11, a fixing pin 12 to fix thesubstrate 52 at a correct position upright stands, spacers 13 are fixedon both the sides of the substrate 52 by fixing pins 14, and guide pins15 are upright standing in four directions of the substrate 52.

Guide holes 22 are formed at a position corresponding to the guide pins15 in the press plate 21, and the guide pins 15 are loosely fitted inthe guide holes 22, respectively, and the press plate 21 is positionedsuch that the press plate 21 is vertically movable with respect to thebase 11. The guide holes 22 serves as a positioning guide for regulatinghorizontal movement of the press plate 21. The press plate 21 operatesas a heavy weight, and, as will be described later, forcibly presses thesemiconductor 50 to the substrate 52.

The flip chip mounting method by the no-flow underfill according to thepresent invention will be described below. FIG. 2 is an explanatorypattern diagram showing an enlarged and magnified main part of thereflow jig 10 in an assembling state. A substrate 52 is fixed at apredetermined position on the base 11, and an epoxy-based resin 54highly filled with the filler 55 is applied in advance to a surface ofthe substrate 52 on which a pad electrode 53 is formed.

The semiconductor 50 is arranged on the upper portion of the substrate52 applied with the resin 54, a bump 51 formed on a rear surface of thesemiconductor 50 and the pad electrode 53 on the substrate 52 arevertically opposite to each other through the resin 54 withoutdisplacement. The press plate 21 larger than the overall size of theproduct of the substrate 52 is placed on the upper portion of thesemiconductor 50.

The press plate 21 operates as a heavy weight which forcibly presses thesemiconductor 50 to the substrate 52 to cause the bump 51 of thesemiconductor 50 to spread out the pre-coated resin 54, and, as shown inFIG. 3, the bump 51 and the pad electrode 53 are brought into contactwith each other. In this state, when the resultant structure is heatedby a reflow soldering process, as shown in FIG. 4, the bump 51 is joinedto the pad electrode 53 of the substrate 52 by thermal welding, and theresin 54 is cured to protect the circumferences of the bump 51 and thepad electrode 53.

The spacer 13 is formed between the lower surface of the press plate 21and the upper surface of the base 11. When the press plate 21 is broughtinto contact with the spacer 13, dropping of the press plate 21 isstopped. For this reason, the weight of a heavy weight 56 does notcontinuously operate after the bump 51 is thermally welded on the padelectrode 53. In this manner, since the amount of press force of thepress plate 21 is regulated by the spacer 13, the bump 51 can beprevented from being broken by pressure, or an electric short circuitcan be prevented from being caused by running the bump 51 out of the padelectrode 53.

As shown in FIG. 5, even though the filler 55 mixed in the resin 54 issandwiched between the bump 51 and the pad electrode 53, the press plate21 forcibly presses the semiconductor 50 to the substrate 52, the filler55 is pressed out of a portion between the bump 51 and the pad electrode53. As shown in FIG. 3, the bump 51 is reliably joined to the padelectrode 53 by thermal welding.

As shown in FIG. 6, the sandwiched filler 55 is pressed from upwardwhile being convoluted between the bump 51 and the pad electrode 53, andthe bump 51 is reliably joined to the pad electrode 53 by thermalwelding. In this case, since the amount of press force of the pressplate 21 is regulated by the spacers 13, the bump 51 is not broken bypressure, or electrical short circuit is not caused by running the bumpout of the pad electrode 53.

In this manner, the semiconductor 50 can be reliably mounted by usingthe resin 54 highly filled with the filler 55, the method can contributeto improvement of workability and reliability in the flip chip mountingmethod by the no-flow underfill.

Various modifications of the present invention can be effected withoutdeparting from the spirit and scope of the present invention. It isnatural that the present invention covers the modifications.

1. A flip chip mounting method by a no-flow underfill in which a resinis pre-coated on a substrate, and, thereafter, a semiconductor with bumpis mounted on the substrate to join a pad electrode on the substrate tothe bump, wherein a flip chip mounting method by a no-flow underfillcomprises a level control function wherein the substrate is placed on anupper surface of a base of a reflow jig, a resin highly filled with thefiller is applied to the substrate, the semiconductor with bump ismounted on a predetermined position of the substrate, a heavy weightlarger than an overall size of a product of the substrate is placed onan upper portion of the semiconductor, a spacer is interposed between alower surface of the heavy weight and an upper surface of the base toregulate an amount of press force of the heavy weight, and horizontalmovement of the heavy weight is regulated by a positioning guide uprightstanding on the upper surface of the base.
 2. A flip chip mountingmethod for mounting a semiconductor with a bump onto a substrate havinga pad electrode comprising the steps of: placing a substrate having padelectrodes on a base; pre-coating a resin on the substrate; placing asemiconductor with bumps in a predetermined position over the substratehaving the pad electrodes positioned under the bumps on thesemiconductor; applying a press plate having guide holes to an upperportion of the semiconductor, whereby the press plate is verticallymovable and a press force is applied to the semiconductor; positioning aspacer between the base and the press plate regulating the verticalmovement of the press plate, whereby contact with the bump and the padelectrode is regulated; and regulating horizontal movement of the pressplate with guide pins mounted on the base corresponding to the guideholes, whereby the bump is brought into reliable contact with the padelectrode.
 3. A flip chip mounting reflow jig for mounting asemiconductor with a bump onto a substrate having a pad electrodecomprising: a base; at least two spacers placed on said base; asubstrate placed on said base between said at least two spacers adaptedto receive a semiconductor having bumps; a plurality of pad electrodesformed on said substrate; a plurality of guide pins placed onto saidbase; and a press plate having a plurality of guide holes adapted toreceive said plurality of guide pins, said press plate positioned oversaid substrate and said at least two spacers wherein said plurality ofguide pins and the plurality of guide holes mate preventing horizontalmovement, and said at least two spacers permit limited vertical movementof said press plate, whereby said at least two spacers limit thevertical movement of said press plate and said plurality of guide pinsand the plurality of guide holes prevent horizontal movement of saidpress plate resulting in a reliable contact between the bumps and saidplurality of pad electrodes after mounting.